U.S. patent application number 14/436263 was filed with the patent office on 2015-10-22 for lifting device.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. The applicant listed for this patent is KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Hirohiko Ishikawa, Tsutomu Matsuo, Yuki Ueda.
Application Number | 20150300380 14/436263 |
Document ID | / |
Family ID | 50487713 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150300380 |
Kind Code |
A1 |
Ueda; Yuki ; et al. |
October 22, 2015 |
LIFTING DEVICE
Abstract
An electromagnetic switching valve, for which the maximum
opening is set to be small, is disposed on piping between a lift
cylinder and a hydraulic pump motor. A pilot check valve, for which
the maximum opening is set to be larger than the electromagnetic
switching valve, is disposed on piping, different from the piping,
between the lift cylinder and the hydraulic pump motor. In
addition, during lowering operations, first, the electromagnetic
switching valve is opened, and then after the same is opened, the
pilot check valve is opened after a prescribed time has passed.
Thus, the shock generated when lowering an object to be
raised/lowered is reduced and a fork is operated quickly.
Inventors: |
Ueda; Yuki; (Kariya-shi,
JP) ; Matsuo; Tsutomu; (Kariya-shi, JP) ;
Ishikawa; Hirohiko; (Kariya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOYOTA JIDOSHOKKI |
Kariya-shi, Aichi-ken |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Kariya-shi, Aichi-ken
JP
|
Family ID: |
50487713 |
Appl. No.: |
14/436263 |
Filed: |
October 18, 2012 |
PCT Filed: |
October 18, 2012 |
PCT NO: |
PCT/JP2012/076915 |
371 Date: |
April 16, 2015 |
Current U.S.
Class: |
60/462 |
Current CPC
Class: |
F15B 2211/46 20130101;
F15B 2211/30505 20130101; F15B 2211/3057 20130101; F15B 11/0413
20130101; F15B 2211/355 20130101; F15B 2211/353 20130101; F15B
2211/7052 20130101; B66F 9/22 20130101; F15B 2211/473 20130101;
F15B 2211/30515 20130101; F15B 2211/20569 20130101; F15B 2211/8606
20130101 |
International
Class: |
F15B 11/04 20060101
F15B011/04; B66F 9/22 20060101 B66F009/22 |
Claims
1. A lifting device that lifts and lowers a lifting material by
supplying and discharging hydraulic oil to and from a hydraulic
cylinder, the lifting device comprising: a hydraulic pump that
supplies the hydraulic oil to the hydraulic cylinder; a first oil
passage that connects the hydraulic cylinder and the hydraulic
pump; a second oil passage that connects the hydraulic cylinder and
the hydraulic pump; and an opening-closing unit that opens and
closes the first oil passage and the second oil passage, wherein
the first oil passage has a maximum oil passage area that is
smaller than a maximum oil passage area of the second oil passage,
the first oil passage includes a first portion between the
hydraulic cylinder and the opening-closing unit, and a second
portion between the opening-closing unit and the hydraulic pump,
and the opening-closing unit allows the hydraulic oil to flow
through the first oil passage when the lifting material is lowered,
and after the first oil passage opens, allows the hydraulic oil to
flow through the second oil passage when a first pressure
difference between the first portion and the second portion
decreases to a predetermined pressure difference or less.
2. The lifting device according to claim 1, wherein the
opening-closing unit includes a first direction control valve
arranged in the first oil passage, wherein the first direction
control valve switches a flow direction of the hydraulic oil in the
first oil passage, and a second direction control valve arranged in
the second oil passage, wherein the second direction control valve
switches a flow direction of the hydraulic oil in the second oil
passage, the maximum oil passage area of the first oil passage is
determined by a maximum open degree of the first direction control
valve, the maximum oil passage area of the second oil passage is
determined by a maximum open degree of the second direction control
valve, and the maximum open degree of the first direction control
valve is smaller than the maximum open degree of the second
direction control valve.
3. The lifting device according to claim 2, wherein the hydraulic
oil flows from the hydraulic cylinder toward the hydraulic pump
through the first and second oil passages when the first direction
control valve and the second direction control valve open, thereby
causing the hydraulic oil to function as driving power used for
driving the hydraulic pump as a hydraulic motor so that the
hydraulic motor performs a regeneration operation.
4. The lifting device according to claim 2, wherein the maximum
open degree of the second direction control valve is set to be in a
range of 20 to 50 times larger than the maximum open degree of the
first direction control valve.
5. The lifting device according to claim 2, further comprising a
measurement unit that measures a time elapsed from when the first
direction control valve opens, wherein the opening-closing unit
opens the second direction control valve when the elapsed time
reaches a predetermined time.
6. The lifting device according to claim 2, further comprising: a
third oil passage through which the hydraulic oil that has passed
through the second direction control valve flows; and a switch
valve arranged in the third oil passage, wherein the first
direction control valve is an electromagnetic switch valve, the
second direction control valve is a pilot check valve including a
valve body accommodated in the second direction control valve and a
throttle oil passage formed in the valve body, the opening-closing
unit is configured to open the switch valve, when the switch valve
opens, the hydraulic oil is discharged from the hydraulic cylinder
to the third oil passage through the throttle oil passage, which
generates a second pressure difference between an inflow side and
an outflow side of the throttle oil passage, and the valve body
moves in a direction in which the second oil passage opens in
accordance with the second pressure difference.
7. The lifting device according to claim 6, wherein the switch
valve is set to have a maximum open degree that is smaller than the
maximum open degree of the pilot check valve, and larger than or
equal to the maximum open degree of the first direction control
valve.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a National Stage of International Application No.
PCT/JP2012/076915 filed Oct. 18, 2012, the contents of which are
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to a lifting device that
includes a hydraulic cylinder used for lifting and lowering and
hydraulically drives the hydraulic cylinder to lift and lower a
lifting material.
BACKGROUND ART
[0003] A lifting device may hydraulically drive a hydraulic
cylinder to lift and lower a lifting material. For example, patent
document 1 describes such a known lifting device that is used for a
forklift. A lifting device for a forklift lifts and lowers a fork
(material handler), which serves as a lifting material, by
supplying and discharging hydraulic oil to and from a hydraulic
cylinder. This type of a lifting device includes a switch valve
that controls the hydraulic oil flowing to a hydraulic pipe
arranged between a hydraulic cylinder and the hydraulic pump. The
fork is lifted, lowered, or stopped by controlling the opening and
closing of the switch valve.
[0004] However, the switch valve may have different pressures at an
inflow side and an outflow side of the hydraulic oil. Under this
condition, if the lifting device for a forklift opens the switch
valve to lower the fork, a shock would occur when the hydraulic oil
starts flowing. Such a shock leads to unstable operation of the
fork, which would move a carried cargo.
[0005] The lifting device of patent document 1 includes a means for
solving the above problem. More specifically, the lifting device of
patent document 1 temporarily activates the hydraulic pump to lift
the fork when starting a lowering operation to decrease the
pressure difference.
PRIOR ART DOCUMENT
Patent Document
[0006] Patent Document 1: Japanese Laid-Open Patent Publication No.
2008-7258
SUMMARY OF THE INVENTION
[0007] When starting the present lowering operation, the lifting
device of patent document 1 determines, from the time elapsed from
when the preceding lowering operation ended and the pressure of the
cylinder, how fast and how long the hydraulic pump produces
rotation in a lifting direction. The lifting device of patent
document 1 may obtain a value taken when the cylinder pressure is
pulsating. In such a case, the increased pressure may be excessive
or insufficient. When the increase in the pressure is excessive,
the hydraulic cylinder performs a lifting operation. From this
condition, the lowering operation is performed. This generates a
time lag between when the lowering operation is instructed and when
the lowering operation actually starts. When the increase in the
pressure is insufficient, the hydraulic cylinder performs a
lowering operation without decreasing the pressure difference. This
generates a shock when the hydraulic oil starts flowing.
[0008] It is an object of the present invention to provide a
lifting device that may be readily operated and reduces the shock
that may occur when a lifting material is lowered.
[0009] To achieve the above object, one aspect of the present
invention is a lifting device that lifts and lowers a lifting
material by supplying and discharging hydraulic oil to and from a
hydraulic cylinder. The lifting device includes a hydraulic pump
that supplies the hydraulic oil to the hydraulic cylinder, a first
oil passage that connects the hydraulic cylinder and the hydraulic
pump, a second oil passage that connects the hydraulic cylinder and
the hydraulic pump, and an opening-closing unit that opens and
closes the first oil passage and the second oil passage. The first
oil passage has a maximum oil passage area that is smaller than a
maximum oil passage area of the second oil passage. The first oil
passage includes a first portion between the hydraulic cylinder and
the opening-closing unit and a second portion between the
opening-closing unit and the hydraulic pump. The opening-closing
unit allows the hydraulic oil to flow through the first oil passage
when the lifting material is lowered. After the first oil passage
opens, the opening-closing unit allows the hydraulic oil to flow
through the second oil passage when a first pressure difference
between the first portion and the second portion decreases to a
predetermined pressure difference or less.
[0010] In the above structure, the first oil passage, which has the
small maximum oil passage area, connects first during a lowering
operation. Since the maximum oil passage area of the first oil
passage is small, a flow rate of the hydraulic oil flowing to the
oil passage is limited. Thus, the hydraulic oil does not suddenly
start flowing. Connection of the first oil passage decreases the
pressure difference between the hydraulic cylinder and the
hydraulic pump (first pressure difference between the first portion
and the second portion). After the first oil passage opens, when
the second oil passage, which has the large maximum oil passage
area, opens, the pressure difference has been already decreased
between the hydraulic cylinder and the hydraulic pump. This limits
generation of a shock even when the hydraulic oil suddenly flows,
thereby decreasing a shock that may occur when lowering the lifting
material. Additionally, when the lowering operation starts, the
hydraulic pump is not controlled to perform lifting operation. This
minimizes the time lag from when a lowering operation is instructed
to when the lowering operation is actually performed. Consequently,
the lifting material may be promptly operated.
[0011] Preferably, the opening-closing unit includes a first
direction control valve arranged in the first oil passage and a
second direction control valve arranged in the second oil passage.
The first direction control valve switches a flow direction of the
hydraulic oil in the first oil passage. The second direction
control valve switches a flow direction of the hydraulic oil in the
second oil passage. The maximum oil passage area of the first oil
passage is determined by a maximum open degree of the first
direction control valve. The maximum oil passage area of the second
oil passage is determined by a maximum open degree of the second
direction control valve. The maximum open degree of the first
direction control valve is smaller than the maximum open degree of
the second direction control valve.
[0012] In the above structure, the opening-closing unit includes
the first direction control valve, which has the small maximum open
degree, and the second direction control valve. The maximum open
degree of the second direction control valve is larger than the
maximum open degree of the first direction control valve. After the
first direction control valve opens, the second direction control
valve opens. Thus, a simple structure may be used to promptly
operate the lifting operation while decreasing a shock that may
occur when lowering the lifting material.
[0013] Preferably, the hydraulic oil flows from the hydraulic
cylinder toward the hydraulic pump through the first and second oil
passages when the first direction control valve and the second
direction control valve open, thereby causing the hydraulic oil to
function as driving power used for driving the hydraulic pump as a
hydraulic motor so that the hydraulic motor performs a regeneration
operation.
[0014] In the above structure, electric energy may be efficiently
used resulting from the regeneration operation of the lowering
operation. The maximum open degree of the second direction control
valve is large. Thus, the pressure drop is small when the hydraulic
oil passes through the second direction control valve. This
provides a sufficient torque used for rotating the hydraulic pump
as the hydraulic motor. Consequently, electric energy may be
efficiently obtained from the regeneration operation.
[0015] Preferably, the maximum open degree of the second direction
control valve is set to be in a range of 20 to 50 times larger than
the maximum open degree of the first direction control valve.
[0016] In the above structure, the difference in the maximum open
degree between the first direction control valve and the second
direction control valve is large. This allows a prompt operation
while decreasing a shock that may occur when lowering the lifting
material by controlling the timing for opening the first direction
control valve and the second direction control valve without
proportionally controlling open degrees of the valves.
[0017] Preferably, the lifting device further includes a
measurement unit that measures a time elapsed from when the first
direction control valve opens. The opening-closing unit opens the
second direction control valve when the elapsed time reaches a
predetermined time.
[0018] In the above structure, the timing for opening the second
direction control valve is managed based on time. Thus, the control
may be simplified.
[0019] Preferably, the lifting device further includes a third oil
passage, through which the hydraulic oil that has passed through
the second direction control valve flows, and a switch valve
arranged in the third oil passage. The first direction control
valve is an electromagnetic switch valve. The second direction
control valve is a pilot check valve including a valve body
accommodated in the second direction control valve and a throttle
oil passage formed in the valve body. The opening-closing unit is
configured to open the switch valve. When the switch valve opens,
the hydraulic oil is discharged from the hydraulic cylinder to the
third oil passage through the throttle oil passage, which generates
a second pressure difference between an inflow side and an outflow
side of the throttle oil passage. The valve body moves in a
direction in which the second oil passage opens in accordance with
the second pressure difference.
[0020] In the above structure, the electromagnetic switch valve of
the third oil passage is a means for applying the pilot pressure to
the pilot check valve. This limits an enlargement of the device and
an increase in costs compared to when an electromagnetic switch
valve having a large maximum open degree is employed instead of the
pilot check valve.
Effects of the Invention
[0021] The present invention performs a prompt operation while
decreasing a shock that may occur when a lifting material is
lowered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a circuit diagram of a first embodiment of a
lifting device.
[0023] FIG. 2 is a schematic view schematically showing the
internal structure of a pilot check valve.
[0024] FIG. 3 is a flowchart showing the procedures of
operations.
[0025] FIG. 4 is a circuit diagram of a second embodiment of a
lifting device.
[0026] FIG. 5 is a circuit diagram of a third embodiment of a
lifting device.
[0027] FIG. 6 is a circuit diagram of a fourth embodiment of a
lifting device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0028] A first embodiment of a lifting device that includes a lift
cylinder lifting and lowering a fork of a forklift according to the
present invention will now be described with reference to FIGS. 1
to 3.
[0029] A fork F is arranged at the front of a forklift and serves
as a material handler (lifting material). When a lift lever L
arranged in a cab is operated, a lift cylinder 10, which serves as
a hydraulic cylinder, is extended or retracted to lift and lower
the fork F.
[0030] A hydraulic control mechanism used for operating the lift
cylinder 10 of the present embodiment will now be described with
reference to FIG. 1.
[0031] A main pipe K, which has a closed circuit structure, is
connected to a hydraulic pump motor 11, which functions as a
hydraulic pump and a hydraulic motor. The main pipe K is also
connected to a pipe K1, which serves as a first oil passage. The
pipe K1 forms a passage through which the hydraulic oil is supplied
to and discharged from the lift cylinder 10 and is connected to a
bottom chamber 10a of the lift cylinder 10. The pipe K1 connects
the lift cylinder 10 and the hydraulic pump motor 11. The hydraulic
pump motor 11 is configured to be capable of producing rotation in
two directions. The main pipe K is connected to transmission
openings 11a, 11b of the hydraulic pump motor 11. The transmission
openings 11a, 11b each serve as an inlet or outlet in accordance
with the flow direction of the hydraulic oil.
[0032] The hydraulic pump motor 11 is connected to a lift motor 12
(rotational electric device), which functions as an electric motor
and an electric generator. The lift motor 12 functions as an
electric motor when a coil of a stator (not shown) is energized to
rotate a rotor. The lift motor 12 functions as an electric
generator when rotation of the rotor generates power in the coil of
the stator. The lift motor 12 of the present embodiment functions
as an electric motor when activating the hydraulic pump motor 11 as
a hydraulic pump, and as an electric generator when activating the
hydraulic pump motor 11 as a hydraulic motor.
[0033] Additionally, the main pipe K is connected to a supply pipe
K2. When the lift cylinder 10 performs a lifting operation, the
hydraulic pump motor 11 is activated to draw the hydraulic oil from
an oil tank 13 and deliver the hydraulic oil through the supply
pipe K2. The supply pipe K2 includes a check valve 14 (non-return
valve) that prevents reverse flow from the main pipe K to the oil
tank 13. The main pipe K is also connected to a discharge pipe K3.
When the lift cylinder 10 performs a lowering operation, the
hydraulic pump motor 11 is activated to return the hydraulic oil to
the oil tank 13 through the discharge pipe K3. The discharge pipe
K3 includes a check valve 15 (non-return valve) that prevents
reverse flow from the oil tank 13 to the main pipe K. The discharge
pipe K3 includes a filter 16 between the oil tank 13 and the check
valve 15.
[0034] Additionally, the main pipe K includes a check valve 17
(non-return valve) that prevents reverse flow from the main pipe K,
which is connected to the transmission opening 11a of the hydraulic
pump motor 11, to the main pipe K, which is connected to the
transmission opening 11b of the hydraulic pump motor 11. The check
valve 17 is arranged in an oil passage between the transmission
opening 11a, which may serve as the outlet of the hydraulic pump
motor 11, and the oil tank 13, which stores the hydraulic oil. The
check valve 17 allows the hydraulic oil to flow from an oil passage
located toward the oil tank 13 from the check valve 17 to the main
pipe K located toward the transmission opening 11b of the hydraulic
pump motor 11 from the check valve 17. The main pipe K also
includes a relief valve 18, which prevents an increase in the
pressure.
[0035] The pipe K1, which is connected to the bottom chamber 10a of
the lift cylinder 10, includes an electromagnetic switch valve 19.
The electromagnetic switch valve 19 serves as a first direction
control valve that switches a flow direction of the hydraulic oil
flowing in the first oil passage. The electromagnetic switch valve
19 may be shifted between two positions, namely, a first position
19a and a second position 19b. When a solenoid is not excited, the
electromagnetic switch valve 19 of the present embodiment is set at
the first position 19a and allows the hydraulic oil to flow from
the hydraulic pump motor 11 to the lift cylinder 10. When the
solenoid is excited, the electromagnetic switch valve 19 of the
present embodiment is set at the second position 19b and allows the
hydraulic oil to bidirectionally flow between the hydraulic pump
motor 11 and the lift cylinder 10. The electromagnetic switch valve
19 of the present embodiment is an on-off valve, which adjusts an
open degree in accordance with the excitement (on) and
non-excitement (off) of the solenoid. Thus, the electromagnetic
switch valve 19 of the present embodiment differs from an
electromagnetic proportional valve capable of adjusting the open
degree in a non-stepped manner. The electromagnetic switch valve 19
of the present embodiment forms an opening-closing unit that opens
and closes the pipe K1, which serves as the first oil passage.
[0036] Additionally, the present embodiment includes a pipe K4,
which serves as a second oil passage, arranged separately from the
pipe K1, which serves as the first oil passage. The pipe K4 forms a
passage through which the hydraulic oil is supplied to and
discharged from the lift cylinder 10 and is connected to the bottom
chamber 10a of the lift cylinder 10. The pipe K4 connects the lift
cylinder 10 and the hydraulic pump motor 11. The pipe K4 includes a
pilot check valve 20. The pilot check valve 20 serves as a second
direction control valve that switches a flow direction of the
hydraulic oil flowing in the second oil passage. As schematically
shown in FIG. 2, the pilot check valve 20 of the present embodiment
has a structure in which a main body accommodates a valve body 20a
that includes a throttle oil passage 20b. The throttle oil passage
20b connects the pipe K4 arranged between the pilot check valve 20
and the bottom chamber 10a of the lift cylinder 10 and a spring
chamber 20c accommodated in the main body. The throttle oil passage
20b is formed by a large diameter oil passage 20d that opens to the
spring chamber 20c and a small diameter oil passage 20e that
extends through from the circumferential surface of the valve body
20a toward the large diameter oil passage 20d. The small diameter
oil passage 20e has a small diameter compared to the large diameter
oil passage 20d.
[0037] When the hydraulic pump motor 11 is activated, the hydraulic
oil is discharged from the transmission opening 11a, which serves
as the outlet, and flows through the main pipe K. When receiving
the pressure of the hydraulic oil, the valve body 20a moves. This
opens the pilot check valve 20 and allows the hydraulic oil to flow
to a passage located toward the lift cylinder 10 from the pilot
check valve 20. When deactivation of the hydraulic pump motor 11
stops the flow of the oil passage, the valve body 20a receives an
urging force of a spring arranged in the spring chamber 20c. This
moves the valve body 20a and closes the pilot check valve 20, which
is open. Additionally, when a difference between the pressure of
the pipe K4 located toward the lift cylinder 10 from the pilot
check valve 20 and the pressure of the spring chamber 20c reaches a
predetermined pressure, the valve body 20a receives the pressure
difference. This moves the valve body 20a and opens the pilot check
valve 20. The pilot check valve 20, which is open, flows the
hydraulic oil discharged from the bottom chamber 10a of the lift
cylinder 10 to an oil passage located toward the main pipe K
(hydraulic pump motor 11) from the pilot check valve 20. More
specifically, the pressure difference, which is used as a pressure
for moving the valve body 20a (pilot pressure), opens the pilot
check valve 20. The pilot check valve 20 of the present embodiment
forms an opening-closing unit that opens and closes the pipe K4,
which serves as the second oil passage.
[0038] The spring chamber 20c of the pilot check valve 20 is
connected to a pipe K5, which serves as a third oil passage. The
pipe K5 includes an electromagnetic switch valve 22, which serves
as a switch valve, with a filter 21 arranged between the
electromagnetic switch valve 22 and the spring chamber 20c of the
pilot check valve 20. The pipe K5 is connected to the main pipe K
that is connected to the transmission opening 11a of the hydraulic
pump motor 11. The pipe K5 also serves as a return oil passage.
More specifically, the hydraulic oil, which flows to the pipe K5
from the pilot check valve 20, passes through the electromagnetic
switch valve 22 and returns to the transmission opening 11a of the
hydraulic pump motor 11 through the main pipe K.
[0039] The electromagnetic switch valve 22 may be shifted between
two positions, namely, a first position 22a and a second position
22b. When a solenoid is not excited, the electromagnetic switch
valve 22 of the present embodiment is set at the first position 22a
and allows the hydraulic oil to flow from the pipe K5 to the main
pipe K. When the solenoid is excited, the electromagnetic switch
valve 22 of the present embodiment is set at the second position
22b and allows the hydraulic oil to bidirectionally flow between
the pipe K5 and the main pipe K. The electromagnetic switch valve
22 of the present embodiment is an on-off valve, which adjusts an
open degree in accordance with the excitement (on) and
non-excitement (off) of the solenoid. Thus, the electromagnetic
switch valve 22 of the present embodiment differs from an
electromagnetic proportional valve capable of adjusting the open
degree in a non-stepped manner.
[0040] In the present embodiment, the maximum open degrees of the
electromagnetic switch valve 19, the pilot check valve 20, and the
electromagnetic switch valve 22, are each set as described below.
In the description hereafter, the open degree of each of the
electromagnetic switch valve 19 and the electromagnetic switch
valve 22 become maximal when set at the second positions 19b, 22b,
respectively. The open degree of the pilot check valve 20 is
maximal when the valve body 20a is open. In the present embodiment,
the maximum open degree of the pilot check valve 20 is set to be
larger than the maximum open degree of each of the electromagnetic
switch valves 19, 22. In other words, the maximum open degree of
each of the electromagnetic switch valves 19, 22 is set to be
smaller than the maximum open degree of the pilot check valve 20.
More specifically, the ratio of the maximum open degree of the
electromagnetic switch valve 19 to the maximum open degree of the
pilot check valve 20 is set to be in a range of 1:20 to 1:50. That
is, the maximum open degree of the pilot check valve 20 is set to
be in a range of 20 to 50 times larger than the maximum open degree
of the electromagnetic switch valve 19. The open degree of the
electromagnetic switch valve 19 is set so that a value indicating a
shock that occurs during a lowering operation is below a target
value. The maximum open degree of the electromagnetic switch valve
22 is set to be the same as or larger than the maximum open degree
of the electromagnetic switch valve 19. In the hydraulic control
mechanism of the present embodiment, the maximum open degree of the
electromagnetic switch valve 19 corresponds to the maximum oil
passage area of the first oil passage. The maximum open degree of
the pilot check valve 20 corresponds to the maximum oil passage
area of the second oil passage. Thus, the maximum oil passage area
of the pipe K1, which includes the electromagnetic switch valve 19
and serves as the first oil passage, is smaller than the maximum
oil passage area of the pipe K4, which includes the pilot check
valve 20 and serves as the second oil passage.
[0041] The structure of a controller S of the hydraulic control
mechanism will now be described.
[0042] The controller S is electrically connected to a
potentiometer Lm that detects the amount of operation of the lift
lever L. The controller S controls the rotation speed of the lift
motor 12 based on a detection signal from the potentiometer Lm in
accordance with the operation amount of the lift lever L. The
controller S also controls the open degree of each of the
electromagnetic switch valves 19, 22 during lifting and lowering
operations.
[0043] Additionally, the controller S is electrically connected to
an inverter S1. Power is supplied to the lift motor 12 from a
battery BT installed in the forklift via the inverter S1. Power
generated with the lift motor 12 is stored in the battery BT via
the inverter S1. The forklift of the present embodiment is of a
battery type that travels by supplying power from the battery BT to
a traveling motor, which serves as a motor. In the present
embodiment, the controller S functions as an opening-closing unit
that opens and closes the first oil passage and the second oil
passage by performing open-close control. The controller S also
functions as a measurement unit.
[0044] The operation of the hydraulic control mechanism of the
present embodiment will now be described.
[0045] The operation for lifting the fork F will now be
described.
[0046] When lifting the fork F, the hydraulic oil is supplied to
the bottom chamber 10a of the lift cylinder 10. Thus, the
controller S controls the rotation speeds of the hydraulic pump
motor 11 and the lift motor 12 to perform lifting at a speed that
is in accordance with the operation amount instructed with the lift
lever L. The controller S also sets the electromagnetic switch
valves 19, 22 at the first positions 19a, 22a, respectively. Thus,
the hydraulic oil, which is drawn from the oil tank 13 by the
hydraulic pump motor 11, flows through the main pipe K to the
electromagnetic switch valve 19 and then the bottom chamber 10a.
That is, the direction in which the hydraulic oil flows is the
direction in which the hydraulic oil flows from the oil tank 13 to
the electromagnetic switch valve 19 and then from the
electromagnetic switch valve 19 to the bottom chamber 10a of the
lift cylinder 10. The hydraulic oil, which is drawn from the oil
tank 13 by the hydraulic pump motor 11, flows to the pilot check
valve 20 through the main pipe K. This opens the pilot check valve
20. Consequently, the hydraulic oil flows to the bottom chamber
10a. That is, the direction in which the hydraulic oil flows is the
direction in which the hydraulic oil flows from the oil tank 13 to
the pilot check valve 20 and then from the pilot check valve 20 to
the bottom chamber 10a of the lift cylinder 10. When the hydraulic
oil enters the bottom chamber 10a, the lift cylinder 10 is
extended. This lifts the fork F. The hydraulic pump motor 11
functions as the hydraulic pump during the lifting operation.
[0047] The operation for lowering the fork F will now be described
with reference to FIG. 3.
[0048] When lowering the fork F, the hydraulic oil is discharged
from the bottom chamber 10a of the lift cylinder 10. Thus, the
controller S of the present embodiment opens the electromagnetic
switch valve 19 first when the hydraulic pump motor 11 and the lift
motor 12 are still (when the rotation speed of the pump is zero)
(step S10). More specifically, the controller S excites the
solenoid of the electromagnetic switch valve 19 and shifts the
position to the second position 19b. Consequently, the hydraulic
oil flows from the lift cylinder 10 to the hydraulic pump motor 11
through the pipe K1 and then returns. That is, in step S10, the
controller S opens the electromagnetic switch valve 19 so that the
direction in which the hydraulic oil flows is the direction in
which the hydraulic oil is allowed to flow from the lift cylinder
10 to the hydraulic pump motor 11. The electromagnetic switch valve
19 of the present embodiment is set to have the maximum open degree
that is sufficiently small. This limits the flow rate of the
hydraulic oil returning to the hydraulic pump motor 11 through the
pipe K1. In other words, a small amount of the hydraulic oil flows.
Such a flow rate control of the hydraulic oil performed by the
electromagnetic switch valve 19 gradually decreases the pressure
difference of the electromagnetic switch valve 19 (pilot check
valve 20) between an oil passage located toward the lift cylinder
10 from the electromagnetic switch valve 19 (pilot check valve 20)
and an oil passage located toward the hydraulic pump motor 11 from
the electromagnetic switch valve 19 (pilot check valve 20). The
pressure difference decreases to a predetermined pressure
difference or less. More specifically, the oil passage K1 (oil
passage K4) includes a first portion between the electromagnetic
switch valve 19 (pilot check valve 20) and the lift cylinder 10 and
a second portion between the electromagnetic switch valve 19 (pilot
check valve 20) and the hydraulic pump motor 11. In the oil passage
K1 (oil passage K4), a first pressure difference (second pressure
difference) between the first portion and the second portion is
gradually decreased to the predetermined pressure difference or
less. The maximum open degree of the electromagnetic switch valve
19 is set to be small. Thus, the hydraulic oil does not suddenly
stat flowing when the electromagnetic switch valve 19 opens. This
reduces the shock that may be felt by an operator.
[0049] At the same time as when the electromagnetic switch valve 19
opens, the controller S starts a timer used for measuring elapsed
time (step S20). Then, the controller S determines whether or not
the timer, which was started in step S20, has reached a
predetermined time X (step S30). The time X is set to be short
enough so that the operator does not feel a time lag from when the
operator instructs a lowering operation to when the lowering
operation actually starts. The time X of the present embodiment is
set to be a fixed value defined in a range "from 0.1 to 0.5
seconds". Additionally, the time X is set so that the pressure
difference of the oil passage located toward the lift cylinder 10
from each of the electromagnetic switch valve 19 and the pilot
check valve 20 and the oil passage located toward the hydraulic
pump motor 11 from each of the electromagnetic switch valve 19 and
the pilot check valve 20 is the predetermined pressure difference
or less. The predetermined pressure difference or less only needs
to be a pressure difference in which an operator of the lifting
device (in the present embodiment, forklift) does not feel a shock.
The controller S repeats the process of step S30 when a
determination result of step S30 is NO.
[0050] When the determination result of step S30 is YES, the
controller S opens the electromagnetic switch valve 22 (step S40).
More specifically, the controller S excites the solenoid of the
electromagnetic switch valve 22 and shifts the position to the
second position 22b. The pilot check valve 20 freely opens when the
hydraulic oil flows from the main pipe K, such as during the
lifting operation. The pilot check valve 20 blocks the flow of the
hydraulic oil from the bottom chamber 10a, such as during the
lowering operation. In this case, the application of the
predetermined pilot pressure opens the pilot check valve 20.
[0051] Thus, when the controller S opens the electromagnetic switch
valve 22, the hydraulic oil between the bottom chamber 10a and the
pilot check valve 20 sequentially flows to the spring chamber 20c
and the electromagnetic switch valve 22 through the throttle oil
passage 20b formed in the valve body 20a of the pilot check valve
20. Then, the hydraulic oil returns to the main pipe K (hydraulic
pump motor 11) through the pipe K5. A pressure drop may occur in
the pilot check valve 20 when the hydraulic oil passes through the
throttle oil passage 20b. Such a pressure drop generates a pressure
difference between an oil passage located toward the lift cylinder
10 from the throttle oil passage 20b, which serves as an inflow
side of the throttle oil passage 20b, and an oil passage located
toward the spring chamber 20c from the throttle oil passage 20b,
which serves as an outflow side of the throttle oil passage 20b.
More specifically, the pressure of the oil passage located toward
the spring chamber 20c becomes lower than the pressure of the oil
passage located toward the lift cylinder 10. Thus, the pressure
difference (second pressure difference) generated between the
inflow side and the outflow side of the throttle oil passage 20b
causes the valve body 20a to gradually open. Consequently, the
hydraulic oil discharged from the bottom chamber 10a of the lift
cylinder 10 directly flows to the main pipe K through the pipe
K4.
[0052] If the diameter (minimum diameter) of the small diameter oil
passage 20e, which forms the throttle oil passage 20b, is too large
relative to the maximum open degree of the electromagnetic switch
valve 22, the pressure difference would not be generated between
the inflow side and the outflow side of the throttle oil passage
20b. Thus, the valve body 20a would not open. If the diameter
(minimum diameter) of the small diameter oil passage 20e is too
small, the pressure difference would be too large between the
inflow side and the outflow side of the throttle oil passage 20b.
Thus, the valve body 20a would quickly open. Thus, the diameter
(minimum diameter) of the small diameter oil passage 20e is set to
generate a pressure difference that opens the valve body 20a and to
be suitable for the open degree of the electromagnetic switch valve
22.
[0053] At a timing when the pilot check valve 20 starts to open,
the controller S controls the rotation speeds of the hydraulic pump
motor 11 and the lift motor 12 so that the operation is performed
at the speed instructed in accordance with the operation amount of
the lift lever L.
[0054] In such a control, when opening the pilot check valve 20,
which has the large maximum open degree, the pressure difference
has been decreased by opening the electromagnetic switch valve 19,
which has the small maximum open degree. This limits generation of
a shock caused by a sudden flow of the hydraulic oil when the pilot
check valve 20 opens, that is, degreases a shock that may occur
when the hydraulic oil flows due to the pressure difference between
the oil passage located toward the lift cylinder 10 from the
electromagnetic switch valve 19 (pilot check valve 20) and the oil
passage located toward the hydraulic pump motor 11 from the
electromagnetic switch valve 19 (pilot check valve 20).
[0055] Then, the hydraulic oil discharged from the bottom chamber
10a of the lift cylinder 10 is drawn through the main pipe K into
the transmission opening 11a of the hydraulic pump motor 11. In
this case, the transmission opening 11a functions as the inlet. The
hydraulic pump motor 11 uses the hydraulic oil discharged from the
bottom chamber 10a as driving power and operates as the hydraulic
motor. Consequently, the lift motor 12 functions as the electric
generator. Power generated with the lift motor 12 is stored in the
battery BT via the inverter S1. More specifically, a regeneration
operation is performed when lowering the fork F. The hydraulic oil,
which serves as the driving power of the hydraulic pump motor 11,
flows from the lift cylinder 10 to the hydraulic pump motor 11
through the oil passages, that is, the pipe K1 and the pipe K4,
when the electromagnetic switch valve 19 and the pilot check valve
20 open, respectively.
[0056] Accordingly, the present embodiment has the advantages
described below.
[0057] (1) During the lowering operation, the electromagnetic
switch valve 19, which has the small maximum open degree, opens
first. This opens the oil passage between the lift cylinder 10 and
the hydraulic pump motor 11. Since the electromagnetic switch valve
19 has the small maximum open degree, the flow rate of the
hydraulic oil flowing to the oil passage is limited. Thus, the
hydraulic oil does not suddenly start flowing. Additionally, the
opening of the electromagnetic switch valve 19 decreases the
pressure difference between the lift cylinder 10 and the hydraulic
pump motor 11. After the oil passage opens between the lift
cylinder 10 and the hydraulic pump motor 11, the pilot check valve
20 having the large maximum open degree may open. In this case, if
a predetermined condition is satisfied, the pressure difference has
been already decreased. This limits the generation of a shock even
when the hydraulic oil suddenly flows, thereby decreasing a shock
that may occur when lowering the lifting material.
[0058] (2) Additionally, when the lowering operation starts, the
control for the lifting operation is not performed on the hydraulic
pump motor 11. This minimizes the time lag from when a lowering
operation is instructed to when the lowering operation is actually
performed. Consequently, the lifting material may be promptly
operated.
[0059] (3) During the lowering operation, the regeneration
operation is performed by using the hydraulic oil discharged from
the lift cylinder 10 as the driving power that drives the hydraulic
pump motor 11 as the hydraulic motor. Thus, electric energy may be
efficiently used. In the present embodiment, the maximum open
degree of the pilot check valve 20 is set to be sufficiently large.
Thus, the pressure drop is small when the hydraulic oil passes
through the pilot check valve 20. This provides a sufficient torque
used for rotating the hydraulic pump motor 11 as the hydraulic
motor. Consequently, electric energy may be efficiently obtained
from the regeneration operation.
[0060] (4) The difference in the maximum open degree between the
electromagnetic switch valve 19 and the pilot check valve 20 is set
to be large. This promptly operates the fork F while decreasing a
shock that may occur when lowering the lifting material by
controlling the timing for opening the electromagnetic switch valve
19 and the pilot check valve 20 without proportionally controlling
open degrees of the valves.
[0061] (5) The valve open degree of an electromagnetic proportional
valve may be proportionally controlled. When such an
electromagnetic proportional valve is employed, the pressure
difference may be decreased by adjusting the open degree of the
electromagnetic proportional valve without using the
electromagnetic switch valve 19, the pilot check valve 20, and the
electromagnetic switch valve 22. That is, a shock that may occur
during the lowering operation would be decreased. However, an
electromagnetic proportional valve is expensive. Additionally, a
current amplifier is needed to drive a proportional valve when an
electromagnetic proportional valve is employed. Thus, the overall
cost would increase. Moreover, the hydraulic control mechanism
would be enlarged. Thus, the present embodiment, which uses no
electromagnetic proportional valve, limits an increase in
costs.
[0062] (6) In particular, when a regeneration operation is
performed during the lowering operation, the regeneration is more
efficient when an on-off valve (electromagnetic switch valve 19) is
employed than when an electromagnetic proportional valve is
employed. Thus, the structure of the present embodiment may
increase the efficiency of the regeneration operation while
reducing a shock.
[0063] (7) The timing for opening the pilot check valve 20 is
time-managed. This eliminates a need for various kinds of sensors,
which are needed when the timing for opening the valve is managed
using pressure, flow rate, or the like. Thus, the structure and
control may be simplified.
[0064] (8) The electromagnetic switch valve 22 is used to control
the opening of the pilot check valve 20. More specifically, the
electromagnetic switch valve 22 is the means for applying the pilot
pressure to the pilot check valve 20. This limits an enlargement of
the device and an increase in costs compared to when an
electromagnetic switch valve having a large maximum open degree is
employed instead of the pilot check valve 20. Additionally, there
is no need to set the electromagnetic switch valve 22 to have a
large maximum open degree. This reduces consumption of power needed
for controlling the opening of the valve.
Second Embodiment
[0065] A second embodiment of the present invention will now be
described with reference to FIG. 4. In the embodiment described
below, the same reference symbols are given to those components
having the same structure as the embodiment that has been
described. Such components will not be described in detail.
[0066] The hydraulic control mechanism of the present embodiment
includes the pipe K4 serving as the second oil passage, which is
arranged separately from the pipe K1 and forms the passage through
which the hydraulic oil is supplied to and discharged from the lift
cylinder 10. The pipe K4 includes an electromagnetic switch valve
23, which serves as the second direction control valve that
switches a flow direction of the hydraulic oil in the second oil
passage. When a solenoid is not excited, the electromagnetic switch
valve 23 of the present embodiment is set at a first position 23a
and allows the hydraulic oil to flow from the hydraulic pump motor
11 to the lift cylinder 10. When the solenoid is excited, the
electromagnetic switch valve 23 of the present embodiment is set at
a second position 23b and allows the hydraulic oil to
bidirectionally flow between the hydraulic pump motor 11 and the
lift cylinder 10. The electromagnetic switch valve 23 of the
present embodiment is an on-off valve, which adjusts an open degree
in accordance with the excitement (on) and non-excitement (off) of
the solenoid. Thus, the electromagnetic switch valve 23 of the
present embodiment differs from an electromagnetic proportional
valve capable of adjusting the open degree in a non-stepped manner.
The electromagnetic switch valve 23 of the present embodiment forms
the opening-closing unit that opens and closes the pipe K4, which
serves as the second oil passage.
[0067] In the present embodiment, the maximum open degrees of the
electromagnetic switch valve 19 and the electromagnetic switch
valve 23 are each set as described below. The open degree of the
electromagnetic switch valve 23 becomes maximal when set at the
second position 23b. In the present embodiment, the maximum open
degree of the electromagnetic switch valve 23 is set to be larger
than the maximum open degree of the electromagnetic switch valve
19. In other words, the maximum open degree of the electromagnetic
switch valve 19 is set to be smaller than the maximum open degree
of the electromagnetic switch valve 23. More specifically, the
ratio of the maximum open degree of the electromagnetic switch
valve 19 to the maximum open degree of the electromagnetic switch
valve 23 is set to be in a range of 1:20 to 1:50. That is, the
maximum open degree of the electromagnetic switch valve 23 is set
to be in a range of 20 to 50 times larger than the maximum open
degree of the electromagnetic switch valve 19. In the hydraulic
control mechanism of the present embodiment, the maximum open
degree of the electromagnetic switch valve 19 corresponds to the
maximum oil passage area of the first oil passage. The maximum open
degree of the electromagnetic switch valve 23 corresponds to the
maximum oil passage area of the second oil passage.
[0068] The operation of the hydraulic control mechanism of the
present embodiment will now be described.
[0069] The operation of the hydraulic control mechanism of the
present embodiment differs from the first embodiment in the control
of the electromagnetic switch valve 23. The contents of the control
of the electromagnetic switch valve 19 are the same as the first
embodiment. The controller S of the present embodiment also
functions as the opening-closing unit that opens and closes the
first oil passage and the second oil passage.
[0070] The operation for lifting the fork F will now be
described.
[0071] The controller S controls the rotation speeds of the
hydraulic pump motor 11 and the lift motor 12 so that the fork F is
lifted at a speed that is in accordance with the operation amount
instructed with the lift lever L. The controller S also sets the
electromagnetic switch valves 19, 23 at the first positions 19a,
23a, respectively. Thus, the hydraulic oil, which is drawn from the
oil tank 13 by the hydraulic pump motor 11, flows through the main
pipe K to each of the electromagnetic switch valves 19, 23 and then
the bottom chamber 10a. That is, the direction in which the
hydraulic oil flows is the direction in which the hydraulic oil
flows from the oil tank 13 to each of the electromagnetic switch
valves 19, 23 and then from each of the electromagnetic switch
valves 19, 23 to the bottom chamber 10a of the lift cylinder 10.
When the hydraulic oil enters the bottom chamber 10a, the lift
cylinder 10 is extended. This lifts the fork F.
[0072] The operation for lowering the fork F will now be
described.
[0073] The controller S opens the electromagnetic switch valve 19
first when the hydraulic pump motor 11 and the lift motor 12 are
still (when the rotation speed of the pump is zero) (step S10 of
FIG. 3). At the same time as when the electromagnetic switch valve
19 opens, the controller S starts the timer used for measuring
elapsed time (step S20 of FIG. 3).
[0074] When the timer reaches the predetermined time X (determined
YES in step S30 of FIG. 3), the controller S opens the
electromagnetic switch valve 23. More specifically, the controller
S excites the solenoid of the electromagnetic switch valve 23 and
shifts the position to the second position 23b. Consequently, the
hydraulic oil flows from the lift cylinder 10 to the hydraulic pump
motor 11 through the pipe K1 and returns. That is, the controller S
opens the electromagnetic switch valve 23 so that the direction in
which the hydraulic oil flows is the direction in which the
hydraulic oil is allowed to flow from the lift cylinder 10 to the
hydraulic pump motor 11. Additionally, at a timing when the
electromagnetic switch valve 23 opens, the controller S controls
the rotation speeds of the hydraulic pump motor 11 and the lift
motor 12 so that the operation is performed at the speed instructed
in accordance with the operation amount of the lift lever L.
[0075] In the same manner as the first embodiment, in such a
control, when opening the electromagnetic switch valve 23, which
has the large maximum open degree, the pressure difference has been
decreased by opening the electromagnetic switch valve 19, which has
the small maximum open degree. This limits generation of a shock
caused by a sudden flow of the hydraulic oil when the
electromagnetic switch valve 23 opens, that is, decreases a shock
that may occur when the hydraulic oil flows due to the pressure
difference between the oil passage located toward the lift cylinder
10 from the electromagnetic switch valve 19 and the oil passage
located toward the hydraulic pump motor 11 from the electromagnetic
switch valve 19.
[0076] Then, the hydraulic oil discharged from the bottom chamber
10a of the lift cylinder 10 is drawn through the main pipe K into
the transmission opening 11a of the hydraulic pump motor 11. Thus,
the hydraulic pump motor 11 operates as the hydraulic motor.
Consequently, the regeneration operation is performed when lowering
the fork F. The hydraulic oil, which serves as the driving power of
the hydraulic pump motor 11, flows from the lift cylinder 10 to the
hydraulic pump motor 11 through the oil passages, that is, the pipe
K1 and the pipe K4, when the electromagnetic switch valve 19 and
the electromagnetic switch valve 23 respectively open.
[0077] The present embodiment has advantages (1) to (7) of the
first embodiment. In the advantages of the present embodiment, the
"pilot check valve 20" and the "electromagnetic switch valve 22" in
advantages (1) to (7) of the first embodiment are replaced by the
"electromagnetic switch valve 23".
Third Embodiment
[0078] A third embodiment of the present invention will now be
described with reference to FIG. 5.
[0079] In the hydraulic control mechanism of the present
embodiment, an electromagnetic switch valve 25 is arranged in the
pipe K1, which connects the bottom chamber 10a of the lift cylinder
10 and the hydraulic pump motor 11. The electromagnetic switch
valve 25 may be shifted between three positions, namely, a first
position 25a, a second position 25b, and a third position 25c. When
neither a first solenoid 25d nor a second solenoid 25e is excited,
the electromagnetic switch valve 25 of the present embodiment is
set at the first position 25a and allows the hydraulic oil to flow
from the hydraulic pump motor 11 to the lift cylinder 10. When the
first solenoid 25d is excited, the electromagnetic switch valve 25
of the present embodiment is set at the second position 25b and
allows the hydraulic oil to bidirectionally flow between the
hydraulic pump motor 11 and the lift cylinder 10. When the second
solenoid 25e is excited, the electromagnetic switch valve 25 of the
present embodiment is set at the third position 25c and allows the
hydraulic oil to bidirectionally flow between the hydraulic pump
motor 11 and the lift cylinder 10. The electromagnetic switch valve
25 of the present embodiment is an on-off valve, which adjusts an
open degree in accordance with the excitement (on) and
non-excitement (off) of the solenoid. Thus, the electromagnetic
switch valve 25 of the present embodiment differs from an
electromagnetic proportional valve capable of adjusting the open
degree in a non-stepped manner.
[0080] Further, the electromagnetic switch valve 25 of the present
embodiment has different maximum open degrees between the second
position 25b and the third position 25c. More specifically, the
maximum open degree of the third position 25c is set to be larger
than the maximum open degree of the second position 25b. In other
words, the maximum open degree of the second position 25b is set to
be smaller than the maximum open degree of the third position 25c.
The ratio of the maximum open degree of the second position 25b to
the maximum open degree of the third position 25c is set to be in a
range of 1:20 to 1:50. That is, the maximum open degree of the
third position 25c is set to be in a range of 20 to 50 times larger
than the maximum open degree of the second position 25b. The
relationship of the maximum open degree of the second position 25b
and the maximum open degree of the third position 25c is the same
as the relationship of the maximum open degrees of the
electromagnetic switch valve 19 and the electromagnetic switch
valve 22 of the first embodiment and the relationship of the
maximum open degrees of the electromagnetic switch valve 19 and the
electromagnetic switch valve 23 of the second embodiment.
[0081] The hydraulic control mechanism of the present embodiment
includes a first oil passage and a second oil passage. The first
oil passage is formed by the pipe K1 and connects the lift cylinder
10 and the hydraulic pump motor 11 via the electromagnetic switch
valve 25 when set at the second position 25b. The second oil
passage is formed by the pipe K1 and connects the lift cylinder 10
and the hydraulic pump motor 11 via the electromagnetic switch
valve 25 when set at the third position 25c. In the electromagnetic
switch valve 25 of the hydraulic control mechanism of the present
embodiment, the maximum open degree of the second position 25b is
smaller than that of the third position 25c. Thus, when configured
in the above manner, the maximum oil passage area of the first oil
passage is smaller than the maximum oil passage area of the second
oil passage. The electromagnetic switch valve 25 forms an
opening-closing unit that opens and closes each of the first oil
passage and the second oil passage. The electromagnetic switch
valve 25 of the present embodiment serves as the first direction
control valve when set at the second position 25b, and serves as
the second direction control valve when set at the third position
25c. Thus, the electromagnetic switch valve 25 includes both the
first direction control valve and the second direction control
valve.
[0082] The operation of the hydraulic control mechanism of the
present embodiment will now be described.
[0083] The operation of the hydraulic control mechanism of the
present embodiment differs from the first and second embodiments in
that the electromagnetic switch valve 25 is controlled. The
controller S of the present embodiment also functions as the
opening-closing unit that opens and closes the first oil passage
and the second oil passage.
[0084] The operation for lifting the fork F will now be
described.
[0085] The controller S controls the rotation speeds of the
hydraulic pump motor 11 and the lift motor 12 so that the fork F is
lifted at a speed that is in accordance with the operation amount
instructed with the lift lever L. The controller S also sets the
electromagnetic switch valve 25 at the first position 25a. Thus,
the hydraulic oil, which is drawn from the oil tank 13 by the
hydraulic pump motor 11, flows through the main pipe K to the
electromagnetic switch valve 25 and then to the bottom chamber 10a.
That is, the direction in which the hydraulic oil flows is the
direction in which the hydraulic oil flows from the oil tank 13 to
the electromagnetic switch valve 25 and then from the
electromagnetic switch valve 25 to the bottom chamber 10a of the
lift cylinder 10. When the hydraulic oil enters the bottom chamber
10a, the lift cylinder 10 is extended. This lifts the fork F.
[0086] The operation for lowering the fork F will now be
described.
[0087] The controller S opens the electromagnetic switch valve 25
at the second position 25b when the hydraulic pump motor 11 and the
lift motor 12 are still (when the rotation speed of the pump is
zero). At the same time as when the electromagnetic switch valve 25
opens at the second position 25b, the controller S starts the timer
used for measuring the elapsed time. When the timer reaches the
predetermined time X, the controller S shifts the electromagnetic
switch valve 25 from the second position 25b to the third position
25c. Thus, the electromagnetic switch valve 25 opens at the third
position 25c. In the hydraulic control mechanism of the present
embodiment, the hydraulic oil flows from the lift cylinder 10 to
the hydraulic pump motor 11 through the pipe K1 and one of the
second position 25b and the third position 25c of the
electromagnetic switch valve 25. This returns the hydraulic oil to
the hydraulic pump motor 11. That is, the controller S opens the
electromagnetic switch valve 25 at one of the second position 25b
and the third position 25c so that the direction in which the
hydraulic oil flows is the direction in which the hydraulic oil is
allowed to flow from the lift cylinder 10 to the hydraulic pump
motor 11. Additionally, at a timing when the electromagnetic switch
valve 25 opens at the third position 25c, the controller S controls
the rotation speeds of the hydraulic pump motor 11 and the lift
motor 12 so that the operation is performed at the speed instructed
in accordance with the operation amount of the lift lever L.
[0088] In the same manner as the first and second embodiments, in
such a control, when opening the electromagnetic switch valve 25 at
the third position 25c, which has the large maximum open degree,
the pressure difference has been decreased by opening the
electromagnetic switch valve 25 at the second position 25b, which
has the small maximum open degree. This limits generation of a
shock caused by a sudden flow of the hydraulic oil when the
electromagnetic switch valve 25 opens at the third position 25c,
that is, decreases a shock that may occur when the hydraulic oil
flows due to the pressure difference between the oil passage
located toward the lift cylinder 10 from the electromagnetic switch
valve 25 and the oil passage located toward the hydraulic pump
motor 11 from the electromagnetic switch valve 25.
[0089] Then, the hydraulic oil discharged from the bottom chamber
10a of the lift cylinder 10 is drawn through the main pipe K into
the transmission opening 11a of the hydraulic pump motor 11. Thus,
the hydraulic pump motor 11 operates as the hydraulic motor.
Consequently, the regeneration operation is performed when lowering
the fork F. The hydraulic oil, which serves as the driving power of
the hydraulic pump motor 11, flows from the lift cylinder 10 to the
hydraulic pump motor 11 through the pipe K1 when the
electromagnetic switch valve 25 opens.
[0090] The present embodiment has the advantages described below in
addition to advantages (1) to (7) of the first embodiment. In the
advantages of the present embodiment, the "electromagnetic switch
valve 19" and the "pilot check valve 20" in advantages (1) to (7)
of the first embodiment are replaced by the "electromagnetic switch
valve 25".
[0091] (9) The pipe K1 includes the electromagnetic switch valve 25
capable of opening at the second position 25b and the third
position 25c, which have different maximum open degrees. More
specifically, the single electromagnetic switch valve 25 is
arranged in the oil passage connecting the lift cylinder 10 and the
hydraulic pump motor 11 to control the amount of the hydraulic oil
flowing through the pipe K1. This simplifies the hydraulic control
mechanism. Use of the single electromagnetic switch valve 25 also
simplifies the piping connecting the lift cylinder 10 and the
hydraulic pump motor 11.
Fourth Embodiment
[0092] A fourth embodiment of the present invention will now be
described with reference to FIG. 6.
[0093] The hydraulic control mechanism of the present embodiment
includes an electromagnetic switch valve 26 arranged in the pipe
K1, which connects the bottom chamber 10a of the lift cylinder 10
and the hydraulic pump motor 11. The electromagnetic switch valve
26 serves as the first direction control valve, which switches a
flow direction of the hydraulic oil in the first oil passage. The
electromagnetic switch valve 26 of the present embodiment is a
four-port valve and arranged in the pipe K5, which connects the
main pipe K and the oil tank 13, in addition to the pipe K1. The
electromagnetic switch valve 26 may be shifted between two
positions, namely, a first position 26a and a second position 26b.
When a solenoid is not excited, the electromagnetic switch valve 26
of the present embodiment is set at the first position 26a and
allows the hydraulic oil to flow in one direction. When the
solenoid is excited, the electromagnetic switch valve 26 of the
present embodiment is set at the second position 26b and allows the
hydraulic oil to flow in two directions. The electromagnetic switch
valve 26 of the present embodiment is an on-off valve, which
adjusts an open degree in accordance with the excitement (on) and
non-excitement (off) of the solenoid. Thus, the electromagnetic
switch valve 26 of the present embodiment differs from an
electromagnetic proportional valve capable of adjusting the open
degree in a non-step manner.
[0094] Additionally, the hydraulic control mechanism of the present
embodiment includes the pilot check valve 20 arranged in the pipe
K4, which connects the bottom chamber 10a of the lift cylinder 10
and the hydraulic pump motor 11. The spring chamber 20c of the
pilot check valve 20 is connected to a pressure compensation valve
27, which serves as a switch valve, via the filter 21. The specific
configuration of the pilot check valve 20 is as illustrated in the
first embodiment with reference to FIG. 2. Thus, the configuration
is the same as the first embodiment.
[0095] The pressure compensation valve 27 may be shifted between
two positions, namely, a first position 27a and a second position
27b. The pressure compensation valve 27 is connected to the pipe K5
located between the main pipe K and the electromagnetic switch
valve 26 and the pipe K5 located between the electromagnetic switch
valve 26 and the oil tank 13. The pressure compensation valve 27 is
normally set at the first position 27a. When the pressure of the
pipe K5 increases between the electromagnetic switch valve 26 and
the oil tank 13, the pressure compensation valve 27 shifts from the
first position 27a to the second position 27b. When set at the
first position 27a, the pressure compensation valve 27 allows the
hydraulic oil to flow to the pipe K5 located between the main pipe
K and the electromagnetic switch valve 26. When set at the second
position 27b, the pressure compensation valve 27 allows the
hydraulic oil to flow in two directions.
[0096] In the present embodiment, the maximum open degree of each
of the electromagnetic switch valve 26 and the pilot check valve 20
is set as described below. In the description hereafter, the open
degree of the electromagnetic switch valve 26 becomes maximal when
set at the second position 26b. Also, the open degree of the pilot
check valve 20 is maximal when the valve body 20a is open. In the
present embodiment, the maximum open degree of the pilot check
valve 20 is set to be larger than the maximum open degree of the
electromagnetic switch valve 26. In other words, the maximum open
degree of the electromagnetic switch valve 26 is set to be smaller
than the maximum open degree of the pilot check valve 20. More
specifically, the ratio of the maximum open degree of the
electromagnetic switch valve 26 to the maximum open degree of the
pilot check valve 20 is set to be in a range of 1:20 to 1:50. That
is, the maximum open degree of the pilot check valve 20 is set to
be in a range of 20 to 50 times larger than the maximum open degree
of the electromagnetic switch valve 26. The relationship of the
maximum open degree of the electromagnetic switch valve 26 and the
maximum open degree of the pilot check valve 20 is the same as the
relationship of the maximum open degrees of the electromagnetic
switch valve 19 and the pilot check valve 20 of the first
embodiment.
[0097] In the hydraulic control mechanism of the present
embodiment, the maximum open degree of the electromagnetic switch
valve 26 corresponds to the maximum oil passage area of the first
oil passage. The maximum open degree of the pilot check valve 20
corresponds to the maximum oil passage area of the second oil
passage. Thus, the pipe K1, which includes the electromagnetic
switch valve 26 and serves as the first oil passage, has the
maximum oil passage area that is smaller than the maximum oil
passage area of the pipe K4, which includes the pilot check valve
20 and serves as the second oil passage. In the same manner as the
first embodiment, the present embodiment includes the
opening-closing unit formed by the electromagnetic switch valve 26,
which opens and closes the pipe K1 serving as the first oil
passage, the pilot check valve 20, which opens and closes the pipe
K4 serving as the second oil passage, and the controller S, which
controls the opening and closing.
[0098] The operation of the hydraulic control mechanism of the
present embodiment will now be described.
[0099] The operation for lifting the fork F will now be
described.
[0100] The controller S controls the rotation speeds of the
hydraulic pump motor 11 and the lift motor 12 to perform lifting at
a speed that is in accordance with the operation amount instructed
with the lift lever L. The controller S also sets the
electromagnetic switch valve 26 at the first position 26a. Thus,
the hydraulic oil, which is drawn from the oil tank 13 by the
hydraulic pump motor 11, flows through the main pipe K to the
electromagnetic switch valve 26 and then the bottom chamber 10a.
That is, the direction in which the hydraulic oil flows is the
direction in which the hydraulic oil flows from the oil tank 13 to
the electromagnetic switch valve 26 and then from the
electromagnetic switch valve 26 to the bottom chamber 10a of the
lift cylinder 10. When the hydraulic oil enters the bottom chamber
10a, the lift cylinder 10 is extended. This lifts the fork F.
[0101] The operation for lowering the fork F will now be
described.
[0102] When the hydraulic pump motor 11 and the lift motor 12 are
still (when the rotation speed of the pump is zero), the
electromagnetic switch valve 26 is set at the first position 26a.
The hydraulic oil does not flow from the bottom chamber 10a of the
lift cylinder 10 to the pipe K1. Additionally, the pressure
compensation valve 27 is set at the first position 27a. This
connects the bottom chamber 10a of the lift cylinder 10 and a pipe
K6 of the pressure compensation valve 27 via the throttle oil
passage 20b, which includes the small diameter oil passage 20e of
the pilot check valve 20. Thus, the pressure of the pipe K6 is the
same as the pressure of the bottom chamber 10a. The pressure of the
pipe K6 sets the pressure compensation valve 27 at the first
position 27a. The hydraulic oil does not flow from the pipe K6 to
the pipe K5.
[0103] When the lowering operation is instructed, the controller S
opens the electromagnetic switch valve 26 at the second position
26b. At same time as when the electromagnetic switch valve 26 opens
at the second position 26b, the controller S starts the timer used
for measuring elapsed time. When the electromagnetic switch valve
26 is open at the second position 26b, the hydraulic oil of the
bottom chamber 10a passes through the electromagnetic switch valve
26, the maximum open degree of which is set to be small. This
increases the pressure of the oil passage located toward the
hydraulic pump motor 11 from the electromagnetic switch valve 26,
thereby gradually decreasing the pressure difference at the inflow
side and the outflow side of the electromagnetic switch valve 26
set at the second position 26b. Consequently, the pressure
difference decreases to the predetermined pressure difference or
less. The maximum open degree of the electromagnetic switch valve
26 is set to be small. Thus, the hydraulic oil does not suddenly
start flowing when the electromagnetic switch valve 26 opens. This
reduces a shock that may be felt by an operator.
[0104] When the electromagnetic switch valve 26 opens at the second
position 26b, the pressure of the pipe K1 increases. This increases
the pressure of the pipe K5, which is also open via the
electromagnetic switch valve 26. The increased pressure of the pipe
K5 triggers a shift of the pressure compensation valve 27 from the
first position 27a to the second position 27b. Thus, when the
pressure difference between the pipe K5 and the pipe K6 decreases
to the fixed value or less, the pressure compensation valve 27
shifts to the second position 27b. When the pressure compensation
valve 27 shifts to the second position 27b, the hydraulic oil flows
to the pipe K5 through the throttle oil passage 20b, which includes
the small diameter oil passage 20e of the pilot check valve 20.
Then, a pressure drop occurs in the small diameter oil passage 20e.
This pushes the valve body 20a of the pilot check valve 20 in the
direction in which the pipe K4 opens. Consequently, the pilot check
valve 20 opens. That is, the pressure drop that occurs when the
hydraulic oil passes through the throttle oil passage 20b generates
a pressure difference between the oil passage located toward the
lift cylinder 10, which serves as the inflow side of the throttle
oil passage 20b, and the oil passage located toward the spring
chamber 20c, which serves as the outflow side of the throttle oil
passage 20b. More specifically, the pressure of the spring chamber
20c is lower than the pressure of the oil passage located toward
the lift cylinder 10 from the pilot check valve 20. Thus, the
pressure difference generated between the inflow side and the
outflow side of the throttle oil passage 20b causes the valve body
20a to gradually open. Consequently, the hydraulic oil discharged
from the bottom chamber 10a of the lift cylinder 10 directly flows
to the main pipe K through the pipe K4.
[0105] When a value measured by the timer reaches a fixed value,
the controller S controls the rotation speeds of the hydraulic pump
motor 11 and the lift motor 12 to perform lifting at a speed that
is in accordance with the operation amount instructed with the lift
lever L. In the hydraulic control mechanism of the present
embodiment, the time when the pilot check valve 20 opens is
calculated in advance through simulations. Then, the fixed value
described above is set to be larger than or equal to the calculated
value. The fixed value is also the time when the pressure
difference between the oil passage located toward the lift cylinder
10 from the pilot check valve 20 and the oil passage located toward
the hydraulic pump motor 11 from the pilot check valve 20 decreases
to the predetermined pressure difference or less.
[0106] In such a control, when opening the pilot check valve 20,
which has the large maximum open degree, the pressure difference
has been decreased by opening the electromagnetic switch valve 26,
which has the small maximum open degree. This limits generation of
a shock caused by a sudden flow of the hydraulic oil when the pilot
check valve 20 opens, that is, decreases a shock that may occur
when the hydraulic oil flows due to the pressure difference between
the oil passage located toward the lift cylinder 10 and the oil
passage located toward the hydraulic pump motor 11 from the
electromagnetic switch valve 26.
[0107] Then, the hydraulic oil discharged from the bottom chamber
10a of the lift cylinder 10 is drawn through the main pipe K into
the transmission opening 11a of the hydraulic pump motor 11. In
this case, the transmission opening 11a functions as the inlet. The
hydraulic pump motor 11 uses the hydraulic oil discharged from the
bottom chamber 10a as driving power and operates as the hydraulic
motor. Consequently, the lift motor 12 functions as the electric
generator. Power generated with the lift motor 12 is stored in the
battery BT via the inverter S1. More specifically, a regeneration
operation is performed when lowering the fork F. The hydraulic oil,
which serves as the driving power of the hydraulic pump motor 11,
flows from the lift cylinder 10 to the hydraulic pump motor 11
through the oil passages, that is, the pipe K1 and the pipe K4,
when the electromagnetic switch valve 26 and the pilot check valve
20 respectively open.
[0108] The present embodiment has the advantages described below in
addition to advantages (1) to (8) of the first embodiment. In the
advantages of the present embodiment, the "electromagnetic switch
valve 19" and the "electromagnetic switch valve 22" in advantages
(1) to (8) of the first embodiment are replaced by the
"electromagnetic switch valve 26" and the "pressure compensation
valve 27", respectively.
[0109] (10) The pressure compensation valve 27 shifts between the
first position 27a and the second position 27b in accordance with
the pressure of the pipe K5. The pressure compensation valve 27
controls the opening and closing of the pilot check valve 20. Thus,
the electromagnetic switch valve 26 is a single direction control
valve the opening and closing of which is controlled by the
controller S. This simplifies the hydraulic control mechanism.
Also, use of the single electromagnetic switch valve 26 limits an
increase in costs of the hydraulic control mechanism.
[0110] Each embodiment may be modified as follows.
[0111] In the first to the third embodiments, at the same time as
when the electromagnetic switch valves 22, 23, 25 open, the
hydraulic pump motor 11 and the lift motor 12 may be operated at a
speed that is in accordance with the operation amount instructed
with the lift lever L.
[0112] In the first and the second embodiments, after the
electromagnetic switch valve 19 opens, the electromagnetic switch
valves 22, 23 may open when a condition is satisfied. The condition
includes the flow rate of the hydraulic oil flowing to the
hydraulic pump motor 11 and the decrease of the pressure difference
between the inflow side and the outflow side of the electromagnetic
switch valve 19. In the third embodiment, after the electromagnetic
switch valve 25 shifts to the second position 25b, the
electromagnetic switch valve 25 may shift to the third position 25c
when a condition is satisfied. The condition includes the flow rate
of the hydraulic oil flowing to the hydraulic pump motor 11 and the
decrease of the pressure difference between the inflow side and the
outflow side of the electromagnetic switch valve 25.
[0113] Each of the embodiments may be configured so that the
electromagnetic switch valves 19, 22, 23, 25, 26 block the oil
passage between the lift cylinder 10 and the hydraulic pump motor
11 when set at the first positions 19a, 22a, 23a, 25a, 26a.
[0114] In the first and the fourth embodiments, the throttle oil
passage 20b formed in the valve body 20a may have any shape and
arrangement.
[0115] In the first embodiment, the pipe K5 may be connected to the
discharge pipe K3 so that the hydraulic oil passing through the
electromagnetic switch valve 22 returns to the oil tank 13.
[0116] The application of the hydraulic control mechanism of each
embodiment is not limited to a forklift. The hydraulic control
mechanism may be applied to an apparatus that performs lowering
operation under its weight (e.g., hydraulic elevator).
DESCRIPTION OF REFERENCE SYMBOLS
[0117] 10 lift cylinder [0118] 11 hydraulic pump motor [0119] 19,
22, 23, 25, 26 electromagnetic switch valve [0120] 20 pilot check
valve [0121] 20a valve body [0122] 20b throttle oil passage [0123]
27 pressure compensation valve [0124] F fork [0125] K1, K4, K5 pipe
[0126] S controller [0127] X time
* * * * *